Traveloka.com and all relevant Indonesian OTA have English version too, normally a foreign credit card should work. For internationals standards executives class is comparable with first class and in my opinion is worth, new economy class now has AC and leather/fabric seats, the amount of space between seats is much better in executive, an average ticket Jogya Bandung can be around 220-260 K IDR in economy and from 300 to 500 K IDR in executive depending on how late you buy the ticket and how full the train is.